Uplink physical channels in the Long Term Evolution (referred to as LTE) system comprise: Physical Random Access Channel (referred to as PARCH), Physical Uplink Shared Channel (referred to as PUSCH), and Physical Uplink Control Channel (referred to as PUCCH). Single-carrier OFDM (Orthogonal Frequency Division Multiplexing) technique is used in the LTE uplink, and the reference signal and data are multiplexed together in the manner of TDM (Time Division Multiplexing). The uplink reference signal comprises demodulation reference signal (referred to as DMRS) and Sounding Reference Signal (referred to as SRS), wherein, said DMRS comprises PUCCH demodulation reference signal and PUSCH demodulation reference signal, which are respectively used for different channel transmission. The main role of the DMRS is for estimation of uplink channels and coherent detection and demodulation of the evolved NodeB (referred to as eNB), and the main role of the SRS is for measurement of uplink channels, whereby, the eNB can perform frequency selective scheduling.
In the LTE (Long Term Evolution) system, in order to achieve and maintain the uplink synchronization between user equipment (referred to as UE) and the evolved NodeB, the evolved NodeB sends Timing Advance (referred to as TA) to each user equipment according to the transmission delay between itself and said user equipment, the user equipment advances or retards its respective uplink transmission timing according to the timing advance sent by the evolved NodeB, so as to compensate for the transmission delay of the user terminal to the evolved NodeB, so that uplink signals of different user equipment can reach the evolved NodeB during the evolved NodeB's receiving window.
The LTE-A (LTE Advanced) system is the next generation of the LTE system, it introduces the concept of Carrier Aggregation. The LTE system bandwidth of said carrier aggregation can be regarded as component carrier frequency spectrum, and each component carrier may also be called a serving cell, that is, one frequency spectrum can be aggregated with a plurality of component carriers (serving cells). One R10 UE resource consists of a plurality of serving cells (component carrier) in the frequency domain, and one cell therein is called the Primary cell (referred to as PCell), and the remaining cells are called Secondary cells (referred to as SCells).
After the introduction of carrier aggregation technology, the user equipment can operate simultaneously on a plurality of component carriers which may be continuous or discontinuous in the frequency band and may also be within the same frequency band or come from different frequency bands. In the case that the component carriers are not continuous, or the component carriers come from different frequency bands, since each component carrier has different transmission characteristics, the timing advances of the component carriers may be different from each other; even if the component carriers belong to the same frequency band and are continuous in the frequency band, if each component carrier comes from different remote radio units (referred to as RRU), or in order to increase the cell coverage, each component carrier is processed respectively via different repeater, then the timing advance of each component carrier may be different. In the LTE system, the UE only operates on one carrier (which is one carrier in the time division duplex mode, and one pair of uplink and downlink carriers in the frequency division duplex mode, for convenience of description, these two cases are herein referred to as a carrier), and only needs to maintain the uplink synchronization of one uplink, while in the carrier aggregation, the UEs can work simultaneously on a plurality of component carriers, and the TAs of these component carriers may be different, that is, there are Multiple Timing Advances (referred to as MTA).
In the scenario of MTA, since the TAs of different uplink component carriers may be different, it means that the signal symbols sent on different uplink component carriers may not be aligned in the time domain, and there may be possibility that the signal symbols sent on different uplink component carriers may be overlapped in the time domain.
In the LTE system, if the transmission power of the signal symbols sent on different uplink component carriers exceeds the maximum transmission power configured by the UE, it needs to reduce the power of the uplink signals. Existing Rel-10 version of the LTE protocol only defines the power reduction method for the case that the uplink signals on multiple uplink carriers are in the same TA, that is, the uplink signal symbols on each uplink carrier are aligned in the time domain. This is specified as follows:
1. When the uplink channels on multiple uplink carriers configured by the UE comprise the PUCCH and the PUSCH, and said PUSCH does not carry the uplink control information (referred to as UCI), the UE does not reduce the transmission power of the PUCCH, but equal-ratio reduces the transmission power of all the PUSCHs, until the transmission power of the UE does not exceed the maximum transmission power configured by the UE.
2. When the uplink channels on multiple uplink carriers configured by the UE are PUSCHs, some of which carry the UCI, the UE does not reduce the transmission power of the PUSCHs carrying the UCI, but equal-ratio reduces the transmission power of all the PUSCHs not carrying the UCI, until the transmission power of the UE does not exceed the maximum transmission power configured by said UE.
3. When the uplink channels on a plurality of uplink carriers configured by the UE are PUSCHs, none of which carries the UCI, the UE equal-ratio reduces the transmission power of all the PUSCHs, until the transmission power of the UE does not exceed the maximum transmission power configured by the UE.
4. When the uplink channels on multiple uplink carriers configured by the UE comprise PUCCHs and PUSCHs, and some of PUSCHs carry the UCI, the UE does not reduce the power of the PUCCHs and the PUSCHs carrying UCI, while equal-ratio reduces the transmission power of the PUSCHs not carrying UCI, until the transmission power of the UE does not exceed the maximum transmission power configured by the UE.
5. When the uplink signals on multiple uplink carriers configured by the UE are SRS, the UE equal-ratio reduces the transmission power of all the SRSs, until the transmission power of the UE does not exceed the maximum transmission power configured by the UE.
Combined with the above description, in the scenario of MTA, if the transmission power of the overlapped symbols in the time domain exceeds the maximum transmission power configured by the UE, it needs to reduce the power of the uplink signals. But in the current Rel-10 and earlier versions of the LTE protocol, there is no definition of power reduction method for the case that, when the transmission symbols are overlapped in the time domain, the transmission power of the overlapped symbols exceeds the maximum transmission power configured by the UE. Therefore, to ensure the normal operation of the carrier aggregation system configured with MTA, it requires to define a power reduction method in the scenario of MTA, when the signal symbols sent on different uplink component carriers overlap in the time domain, and the transmission power of the overlapped symbols exceeds the maximum transmission power configured by the UE.